The ballistic cloth refers to a kind of clothing which is developed in order to protect the human body against bullet shells and fragments. Therefore, one of the important requisites of the ballistic cloth is the ballistics performance. As the ballistic composite material is a product which needs to protect the body of soldiers etc. from the bullet or the shell, the ballistics performance depends largely on the material used therein.
Since a high tenacity polyethylene (HMPE, High Molecular Weight Polyethylene), which is one kind of such ballistic composite materials, has a low weight of about 0.98 which is even lower than that of water, it is thus widely used as a ballistic material. But the high tenacity polyethylene has the problem that it is susceptible to deformation in case of a physical impact during use, and that it is vulnerable to heat and ruptures easily.
As a part among the other composite materials for the ballistic composite material, the wholly aromatic polyamide fibers, which are collectively called as an aramid fiber, comprises a para-amide fiber having the structure in which benzene rings are connected through an amide group (—CONH) in a straight forward manner, and a meta-amide fiber which is not so. A para-amide fiber has excellent characteristics including high strength, high elasticity, and low shrinkage, etc., and it has such excellent strength that it can lift a vehicle weighing 2 Tons with a thin yarn which has the thickness of about 5, and is thus being widely used as a composite material for the ballistic composite material.
Such ballistic composite material using the aramid fiber, was commonly manufactured by preparing an aramid textile using an aramid fiber, and by dipping a polymer resin into such aramid textile, and solidifying such semi-cured aramid fabric after laminating it into a mold in multiple layers, thereafter.
Conventionally, in the manufacture of a ballistic cloth, an ultra thin polyethylene film (or ultra thin PE film) was used separately as a protection film, and the ultra thin polyethylene film existed on the surface of a unidirectionally-oriented aramid sheet in the form of a protection film.
In manufacturing the conventional unidirectionally-oriented aramid sheet, after dipping it in a resin, it was given a squeezing in order to fit the uniform resin content. Thereafter, it was manufactured by way of either attaching the ultra thin film thereon, or by using a film binder and then coating a viscoelastic object on the surface of the yarn. But this caused a problem that the manufacturing process became troublesome.
Thus, in the relevant industry, in the manufacture of a sheet using a binder that sticks together the layers of an aramid sheet and a polyethylene film which serves as a surface protection film, it is desperately needed that the manufacturing process is made to be simple and time-efficient, and the technology to improve productivity needs to be developed.